util: document recommended filesystems

In particular, recommend against using exFAT on MacOS as this is known
to cause breakages.

See #31454 for more context.

doc/files.md

@@ -16,6 +16,8 @@
 
 - [Legacy subdirectories and files](#legacy-subdirectories-and-files)
 
+- [Filesystem recommendations](#filesystem-recommendations)
+
 - [Notes](#notes)
 
 ## Data directory location
@@ -123,6 +125,12 @@ Path           | Description | Repository notes
 `addr.dat`     | Peer IP address BDB database; replaced by `peers.dat` in [0.7.0](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.7.0.md) | [PR #1198](https://github.com/bitcoin/bitcoin/pull/1198), [`928d3a01`](https://github.com/bitcoin/bitcoin/commit/928d3a011cc66c7f907c4d053f674ea77dc611cc)
 `onion_private_key` | Cached Tor onion service private key for `-listenonion` option. Was used for Tor v2 services; replaced by `onion_v3_private_key` in [0.21.0](https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.21.0.md) | [PR #19954](https://github.com/bitcoin/bitcoin/pull/19954)
 
+## Filesystem recommendations
+
+When choosing a filesystem for the data directory (`datadir`) or blocks directory (`blocksdir`), some filesystems should be avoided:
+
+- **MacOS**: The exFAT filesystem should not be used. There have been multiple reports of database corruption when using exFAT on MacOS for Bitcoin Core. This appears to be due to filesystem-level issues with exFAT on MacOS. See [Issue #31454](https://github.com/bitcoin/bitcoin/issues/31454) for more details.
+
 ## Notes
 
 <a name="note1">1</a>. The `/` (slash, U+002F) is used as the platform-independent path component separator in this document.

src/common/init.cpp

@@ -79,7 +79,10 @@ std::optional<ConfigError> InitConfig(ArgsManager& args, SettingsAbortFn setting
             FSType fs_type = GetFilesystemType(check.path);
             switch(fs_type) {
                 case FSType::EXFAT:
-                    InitWarning(strprintf(_("Specified %s \"%s\" is exFAT which is known to have intermittent corruption problems on MacOS."), check.description, fs::PathToString(check.path)));
+                    InitWarning(strprintf(_("Specified %s \"%s\" is exFAT which is known to have intermittent corruption problems on MacOS. "
+                        "See https://github.com/bitcoin/bitcoin/blob/master/doc/files.md#filesystem-recommendations for more information."),
+                        check.description,
+                        fs::PathToString(check.path)));
                     break;
                 case FSType::ERROR:
                     LogInfo("Failed to detect filesystem type of %s: %s\n", check.description, fs::PathToString(check.path));